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In the context of global climate change, a significant increase in the active layer thickness (ALT) of permafrost is expected in the current century. This process has been observed by researchers over the past few decades. If the current climate trend continues, an increase in ALT may have a significant impact on the concentration of organic matter in Arctic river waters. The relationship between the thickness of the seasonally thawed layer of permafrost and the concentration of dissolved organic matter in river waters has been explored using clustering, one-way ANOVA, and cross-tabulation analysis. The data set for analysis included original details on the content of organic matter in the rivers of Eastern Siberia (in terms of COD, BOD5, and the color of the water), phytoplankton abundance and biomass, and data on the permafrost active layer thickness (ALT) in the catchments. It was revealed that in the areas of catchments where the ALT is deeper, the content of organic matter in the rivers is lower than in areas with a shallow, seasonally thawed permafrost. Our results are consistent with the existing conceptual model of the influence of ALT on the chemistry of river waters in the cryolithozone. This knowledge is important for predicting the chemical composition of the Arctic rivers, eutrophication, and the rate of inflow of dissolved solids into the Arctic Ocean under the current conditions of ALT deepening.

Large rivers are important links between continents and oceans for material flows that have a global impact on marine biogeochemistry. Processes in the catchment areas of large rivers can affect the flow of solutes into the global ocean. The goal was to determine how the concentration of individual components of nutrients in the rivers of Eastern Siberia changes depending on the active layer thickness of the permafrost (ALT) and to elucidate whether the ALT is a factor that can control nutrient flux to the Arctic Ocean. The method of canonical correlation analysis was applied to the data on the concentration of nutrients in the 12 largest rivers of Eastern Siberia and the active layer thickness in their catchments. We found that the concentration of nutrients such as ammonium ion (NH4) and total phosphorus (Ptotal) in river waters is higher in catchments with a deeper active layer. The waters of the mountain rivers in the south of the region (the Chara and Vitim rivers) are the richest in nutrients. Arctic rivers such as the Indigirka and Anabar were low in nutrients. The permeability of soils also affects the discharge of nutrients into rivers with surface runoff. We conclude that in the future, in the context of global climatic changes and the projected deepening of the active layer throughout the permafrost zone of the Northern Hemisphere, an increase in the supply of nutrients to the Arctic Ocean is possible.